The Quectel EC25 is a LTE Modem Module manufactured by the Chinese Company Quectel. It is available as solder-type version but also as miniPCIe card.

It is based around the Qualcomm MSM 9x70 and runs an OE based Linux distribution on its internal Cortex-A5 core. This Linux on Cortex-A5 is what implements the USB device that you see from the host PC!

Below testing has been made on an EC25-E Revision: EC25EFAR02A03M4G (according to ATI0 and the label on the device)

NOTE: If you use stock Linux, the drivers will have fixed assumptions as to which interface is used by what function! You need to patch your kernel to change that assumption, or ensure that the order of interfaces / interface numbers doesn't change

an application registering a DIAG command with /dev/diag. Once that diag command is received, it will write to /dev/rebooterdev which will be picked up by reboot-daemon to actually do the reboot. Weird architecture.